A New Perspective on Hydrogen Chloride Scavenging at High Temperatures for Reducing the Smoke Acidity of PVC Cables in Fires, IV: The Impact of Acid Scavengers at High Temperatures on Flame Retardance and Smoke Emission

In PVC compounds, hydrogen chloride plays a fundamental role in ·H and ·OH radical trapping, lowering the flame energy during combustion. Furthermore, it yields actual Lewis acids promoting the cross-linking of the polyene sequences from PVC degradation and bringing a char layer, protecting PVC items from flames. Therefore, PVC is inherently flame-retarded. However, plasticized PVC requires flame retardants and smoke suppressants to enhance fire performance. Low-smoke acidity PVC compounds have been developed to reduce the HCl emission during combustion and, therefore, the acidity of the smoke. They contain potent acid scavengers capable of acting at high temperatures. They react with hydrogen chloride in the condensed phase, making it unavailable in the gas and even in the condensed phase, compromising the reaction to fire and enhancing the smoke produced during the combustion. The effect of the sequestration of hydrogen chloride in PVC compounds for cables by potent acid scavengers is studied in this paper through measurements of oxygen index, heat release, and smoke production. It is noteworthy that the potent acid scavengers strongly affect parameters such as the oxygen index, the fire growth rate in cone calorimetry, the specific (total) heat capacity, and the specific heat of combustion of fuel gases in micro combustion calorimetry. In some formulations, acid scavengers reduce the oxygen index below the values of the formulations without flame retardants and double their fire growth rate. In fact, they neutralize the action of antimony trioxide and Lewis acid precursors commonly used as flame retardants and smoke suppressants in PVC items, making them prone to ignite, release smoke, and spread flame. A new generation of flame retardants and smoke suppressants is needed to keep together the low-smoke acidity and the fire performance in PVC items.